Method and apparatus for electro-optical distance measurement

• US 4,916,324 A
• Filed: 09/29/1988
• Issued: 04/10/1990
• Est. Priority Date: 10/23/1987
• Status: Expired due to Term

• Current Assignee: Leica Aarau AG
• Original Assignee: Kern AG
• Inventors: Meier, Dietrich
• Primary Examiner(s): Nelms, David C.
• Application Number:
  US07/250,854
• Time in Patent Office: 558 Days
• Field of Search: 250/201 AF, 250/560, 250/561, 356/1, 356/4, 356/5, 356/141, 356/152
• US Class Current: 250/559.38
• CPC Class Codes: G01S 17/08 for measuring distance only indirect measurement G01S17/46; active triangulation systems G01S17/48
• CPC Class Codes: G01S 7/4812 transmitted and received beams following a coaxial path
• CPC Class Codes: G01S 7/499 using polarisation effects

Abstract

To simplify the reflectors for electro-optical distance measurement with a distance measuring apparatus with modulation of light outside of the light source, the optical bundle for distance measurement is focussed on to the target. Thereby, distance measurements on unprepared (non-cooperative) objects or on objects prepared only with simple reflecting foils are made possible.

Claims

1. A method for electro-optical distance measurement employing a distance measuring apparatus, comprising the steps of:

generating a bundle of electromagnetic radiation;

modulating said bundle a first time by means of an electro-optic modulator;

focussing the bundle onto a target;

modulating a second time components of said bundle reflected at said target means; and

measuring the signal strength of said components.

2. A method as claimed in claim 1, wherein the target means is provided with a multitude of reflecting elements within the area receiving said bundle of electromagnetic radiation.

3. A method as claimed in claim 2, wherein said multitude of reflecting elements are provided on a reflecting foil.

4. A method as claimed in claim 1, wherein said electro-optic modulator comprises an electro-optic crystal, by means of which the polarization of said bundle of electromagnetic radiation is modulated.

5. A method as claimed in claim 4, wherein the bundle of electromagnetic radiation is coherent and is modulated for both the first time as well as for the second time by means of only one and the same electro-optic crystal.

6. A method as claimed in claim 5, wherein said coherent bundle of electromagnetic radiation is linearly polarized and is directed successively through a polarizing beam splitter, said electro-optic crystal, a quarterwave plate matched to a wavelength of electromagnetic radiation of said bundle, onto the target means and once more through said quarterwave plate, said electro-optic crystal and said polarizing beam splitter onto a detector of electromagnetic radiation.

7. A method as claimed in claim 6, wherein interference effects between components of radiation scattered at said target means and at said distance measuring apparatus appearing on said detector of electromagnetic radiation are used as a criterion of focussing said bundle of electromagnetic radiation onto said target means.

8. A method as claimed in claim 6, wherein said bundle of electromagnetic radiation is modulated with a varying frequency, and corresponding variations on said detector of components of radiation scattered at the target means are used as a criterion of focussing.

9. An electro-optical distance measuring apparatus comprising:

means for generating a bundle of electromagnetic radiation;

electro-optic modulator means for modulating said bundle a first time;

means for focussing the modulated bundle onto a target; and

means for measuring a signal strength of components of said bundle which have been reflected from said target and modulated a second time by said modulator means.

10. The apparatus according to claim 9, wherein said electro-optic modulator means further comprises an electro-optic crystal, by means of which the polarization of said bundle of electromagnetic radiation is modulated.

11. The apparatus according to claim 10, wherein the bundle of electromagnetic radiation is coherent and is modulated for both the first time as well as for the second time by means of only one and the same electro-optic crystal.

12. The apparatus according to claim 11, wherein said coherent bundle of electromagnetic radiation is linearly polarized and is directed successively through a polarizing beam splitter, said electro-optic crystal, a quarterwave plate matched to a wavelength of electromagnetic radiation of said bundle, onto the target means and once more through said quarterwave plate, said electro-optic crystal and said polarizing beam splitter onto a detector of electromagnetic radiation.

13. The apparatus according to claim 12, wherein interference effects between components of radiation scattered at said target and at said distance measuring apparatus appearing on said detector of electromagnetic radiation are used as a criterion of focussing said bundle of electromagnetic radiation onto said target.

14. The apparatus according to claim 12, wherein said bundle of electromagnetic radiation is modulated with a varying frequency, and corresponding variations on said detector of components of radiation scattered at the target are used as a criterion of focussing.